The present invention relates generally to damping of magnetization changes in magnetic materials. The invention is of particular advantage in any high speed magnetic devices wherein the function of such devices requires changing the magnetization direction of a magnetic layer or other magnetic region of the device.
It has been shown that thin magnetic films of the magnetic transition metal alloys are severely underdamped. For example Silva et. al. J. Appl. Phys. Vol 85 no. 11 p. 7849 (1999) describe magnetization oscillations in thin Permalloy (Ni81Fe19) films after magnetic switching. Myrtle et. al. J. Appl. Phys. Vol. 57, no. 1 p. 3693 (1985), Heinrich et. al. Phys. Rev. Lett. Vol. 59 no. 15 p. 1756 (1987) and Schreiber et. al. Sol St. Comm. Vol. 93 no 12 p 965 (1995) describe measurement results of damping in Ni, Fe, and Co, all with very small magnetic damping parameters. Alloys of these materials also have damping parameters in the same order of magnitude as their constituents, Patton et. al. J. Appl. Phys. Vol. 46 no. 11 p. 5002 (1975) and Schreiber et. al. Sol. St. Comm. Vol. 93 no 12 p 965 (1995).
Any high speed magnetic devices, including spin valves and MTJ""s (magnetic tunnel junctions), that require a fast change in magnetization direction, i.e. switching of magnetization between equilibrium positions, as part of their function will potentially suffer from magnetic oscillations. These magnetic oscillations can in some cases be large enough that the final equilibrium state becomes unpredictable, i.e. the device can relax to the wrong equilibrium state. This obviously causes severe control problems.
It is desireable to adjust the magnetization damping in magnetic devices to reduce magnetic oscillations after switching and to open an opportunity to engineer devices to optimise their time response.
The present invention broadly provides a magnetic device comprising a) at least one electrode and b) a magnetic region comprising an alloy of a magnetic material and a transition metal selected from the 4d transition metals and the 5d transition metals. Preferably, the transition metal is present in an atomic concentration between about 4% and about 15% of the alloy and is selected from among osmium, niobium, ruthenium, rhodium, tantalum, platinum, iridium, palladium, rhenium, molybdenum, and tungsten.
According to a preferred embodiment of the invention, the magnetic device is operable as a spin valve or as a magnetic tunnel junction and comprises at least two magnetic layers and a no magnetic layer there between, wherein the two magnetic layers have at least two stable magnetization relationships, and wherein at least one of said at least two magnetic layers comprises the aforesaid alloy.
According to a second preferred embodiment of the invention, the magnetic device is operable as a magnetic tunnel junction and comprises at least two magnetic layers and an insulating barrier layer there between, wherein the two magnetic layers have at least two stable magnetization relationships, and wherein at least one of said at least two magnetic layers comprises the aforesaid alloy.